Chopping the mains sine wave causes fast voltage and current changes in the dimmer. Unless there is suitable radio interference suppression. high frequency interference would be
caused in the mains wiring. The interference due to the dimmer, consists of the 50/60Hz frequency plus varying amounts of multiples and divisions of the frequency. The multiples can typically range from 30Khz to 1.5Mhz, and the divisions can be down to 20 harmonics
of the original. The house or building wiring acts as an aerial and transmits the
signals into the air. Earth connections that are insufficiently grounded and form
earth loops can also act as aerials. Cheap, poor quality dimmers without sufficient
filtering will cause RF interference. Quality dimmers and lighting controls use RF choke based suppression circuits to limit the rate of rise of current di/dt and capacitors to suppress the higher frequencies.